Correlation between Ornithine Decarboxylase Activity and Toxoplasma gondii Proliferation in Cultured Embrionic Retina

Abstract

Abstract: : Purpose: It is known that Toxoplasma gondii, the most common cause of retinochoroiditis in humans, is an obligate intracellular protozoan parasite, depending of host cells microenvironment to proliferate. The vast majority of the cases of retinochoroiditis in immunocompetent patients result from congenital infection. In this study we decided to investigate the ability of Toxoplasma gondii to infect retinal tissue during development when microenvironment changes normally occur. Methods: Retinas from 5 to 9-day-old chick embryos were used. Stationary cultures were plated in 24 well cell culture cluster and maintained at 37°C in DMEM medium plus 5% fetal bovine serum for 2 to 6 days and then each well were infected with 4 x 10⁵ tachyzoites. Explants of retinas were prepared and maintained in DMEM under rotation at 37°C. Proliferation was measured using [³H]–thymidine incorporation after 72h. Ornithine decarboxylase (ODC) activity was determined by measuring CO₂ production from using [1 –¹⁴C]–ornithine. Results: Proliferation of tachyzoites was high in cultures expressing elevated ODC activity. The addition of ODC inhibitors 48h before and some minutes after infection reduced T. gondii proliferation by approximately 30 to 40%. As for cultured retina cells, retina explants also allowed T. gondii proliferation whenever ODC activity was high. Conclusions: The data suggest a direct correlation between retinal polyamine biosynthesis and the proliferation of T. gondii. This is in agreement with the observation that the majority of retinochoroiditis in immunocompetent patients caused by T. gondii results from congenital infection.

Keywords: retinochoroiditis • toxoplasmosis • retinal culture